The present invention relates to a sliding member.
A swash plate for a compressor is disclosed in JP-A-10-205442, JP-A-11-13638, JP-A-11-193780, JP-A-2001-280236 and JP-A-2002-5013 as an example of a conventional sliding member. The swash plate contains a base material having formed on the surface thereof sliding layers constituting sliding surfaces, on which shoes slide.
The swash plates disclosed in JP-A-10-205442, JP-A-11-13638 and JP-A-11-193780 employ a sliding layer containing a first layer formed on the base material and a second layer formed on the first layer. The base material of the swash plate is ordinarily formed of an iron material, such as spheroidal graphite cast iron (FCD) or bearing steel (SUJ2). The swash plate has the first layer formed of Sn formed by plating, Cu—Sn—Pd formed by thermal spraying or the like, and the second layer formed of polyamideimide (PAI) containing MoS2.
JP-A-2001-280236 and JP-A-2002-5013 disclose a swash plate having a sliding layer containing an amorphous hard carbon (diamond-like carbon (DLC)) film formed on the base material. JP-A-2001-280236 also discloses that the DLC film may contain silicon (Si).
The swash plate is used in a swash plate compressor. The swash plate compressor contains a housing having formed therein cylinder bores, a crank chamber, a suction chamber and a discharge chamber, pistons being reciprocably housed in the each cylinder bore and comparting compression chambers in the each cylinder bore, a driving shaft being driven with an external driving source and being supported rotatably with the housing, and a swash plate being provided inside the crank chamber and converting the rotational movement of the driving shaft to a reciprocal movement of the pistons through each pairs of shoes in contact with front and rear surfaces of the swash plate. An ordinary swash plate is a single member and is rotatable along with the driving shaft in a state where the front and rear surfaces thereof is inclined with respect to the driving shaft. The shoes are each in a substantially hemispherical shape, and the substantially flat surfaces of the shoes are in contact with the front and rear surfaces of the swash plate.
In the swash plate compressor having the structure, the driving shaft is rotated with the external driving source to rotate the swash plate, whereby the pistons are reciprocated in the cylinder bores. According to the operation, the swash plate compressor sucks refrigerant from the suction chamber and compresses the refrigerant in the compression chambers, followed by discharging the refrigerant to the discharge chamber.
The swash plate compressor is used with an evaporator, an expansion valve, a condenser and piping to constitute a refrigeration circuit of a vehicle or the like, thereby attaining air-conditioning in a vehicle interior or the like.
The environment, under which a sliding member is used, is becoming severer owing, for example, to high-speed driving of a swash plate compressor, and there is a demand for a sliding member that is capable of exhibiting excellent sliding property as compared to a conventional product. A swash plate free of lead in a sliding layer is also demanded in view of protection of natural environments. Taking the demands in consideration, the inventors have confirmed the following phenomena associated with the conventional swash plate.
The second layer formed of PAI containing MoS2 in the conventional sliding layer may be peeled off upon long-term use due to unavoidable foreign matters that may present in the crank chamber of the swash plate compressor. The first layer, which is formed of Sn or Cu—Sn—Pb by plating or thermal spraying, is exposed thereby, and is demanded to attain improvement in durability under poor lubrication conditions.
The conventional sliding layer formed of a DLC film exhibits excellent sliding property as compared to the first layer formed of Sn or Cu—Sn—Pb by plating or thermal spraying since the DLC film shows a low friction coefficient under poor lubrication conditions, but under conditions where substantially no lubricating oil is present, the sliding layer slides directly on shoes as counterparts, which brings about possibility of deterioration in durability.
Under the circumstances, the inventors have investigated that a DLC film is used as the first layer of the sliding layer, and PAI containing MoS2 is used as the second layer.
However, the sliding layer is insufficient in adhesion of the second layer. As a countermeasure, the surface of the base material may be roughened for improving the adhesion of the second layer on the first layer formed of a DLC film. In the case where the second layer is peeled off upon long-term use, however, hard protrusions may attack the shoes to impair the sliding property of the shoes with respect to the swash plate, whereby there are problems including sticking of the shoes to the piston, which brings about possibility of deterioration in durability of the swash plate compressor.